The invention pertains to a method and equipment for the polymerization cast molding of articles, above all of lenses from hydrophilic gels.
In the processes hitherto known, the molded articles from hydrogels, above all soft contact lenses, are made by polymerization casting in molds. The volume is reduced under a steep increase of viscosity during polymerization. This contraction gives rise to bubbles and surface depressions in firm molds. The formation of bubbles is prevented in open rotating molds by a free level on the one hand and by the centrifugal force of rotation on the other. However, the apparatuses for polymerization casting of lenses under rotation are rather complicated and have high demands to precision. A certain amount of rejects should be always considered in the industrial production and the articles must be classified on the basis of precise measurements.
Rods and tubes from hydrogels, above all in a nonswollen state, can be produced by the polymerization of a monomer mixtures in elastic molds, for example, in hoses from silicon rubber. Only semiproducts are obtained in this way, which are processed to the required articles by precise mechanical working. The direct cast molding of articles is not concerned in this case.